Overweight and obesity are major health problems, affecting over two-thirds of US adults. Commercially available Internet-based weight loss programs are currently used by millions of overweight/obese individuals in the U.S, but weight losses are often poor, likely because these products on the whole do not incorporate empirically validated behavioral weight loss strategies that have been researched for over 40 years. Similarly, the weight losses obtained via research-based online weight loss programs are about half the size of those obtained via in-person treatment, likely because of the lack of (1) hands-on training in behavioral weight control strategies, and (2) support and guidance from group leaders and peers, both of which are hallmarks of traditional in-person treatment. The goal of this application is to improve commercial Internet -delivered behavioral obesity treatments by developing a virtual reality (VR) system that can be integrated into existing Internet weight control programs, such as Weight Watchers Online. The VR system will allow users to experience learning, implementing, and mastering behavioral weight control strategies in controlled virtual settings with the support of a culturally sensitive virtual coach. The VR system will: (a) increase awareness of barriers to weight control behaviors, (b) teach skills to cope with these barriers, (c) build confidence using these skills, and (d) increase commitment to using these skills in real-world situations. The design of the VR System is based on Social Cognitive Theory, which states that health behaviors are learned by observing and imitating peers and role models, and by receiving social reinforcement. A Phase I application (1R41HL114046- 01) was recently completed successfully by the applicants, in which a prototype VR weight loss intervention, designed for integration with existing Internet-delivered behavioral weight loss programs, was developed and pilot tested with a single VR vignette focused on social eating situations. A virtual coach will was used to lead the user through the vignette, teach the user behavioral weight control strategies, and help the user cope with any consequences of using behavioral weight control strategies. This interactive social eating vignette produced statistically significant improvements in self-reported difficulty controlling eating in social situations, and knowledge, confidence, and commitment for using empirically validated skills for controlling eating in social situations. In this Phase II application we propose to refine the socil eating vignette created and tested in Phase I, and develop an additional 3 vignettes pertaining to other challenging situations involving eating, physical activity, and sedentary behavior (i.e., time spent sitting). We will conduct a randomized controlled trial (RCT) with N = 125 participants to test the efficacy of the 4 vignettes for improving weight losses obtained in a popular paid commercial weight loss program (Weight Watchers Online) over 6 months. Upon successful completion of this Phase II project, we will market the VR system with 4 vignettes to providers of commercially available Internet-based weight loss programs such as Weight Watchers, Inc. (see included letter of support).